Motor frame cooling with hot liquid refrigerant and internal liquid

ABSTRACT

This invention presents the device and method for cooling electric machines with hot liquid refrigerant in a floating refrigerant loop and using an internal liquid such as oil for enhancing the cooling effects. The electric machine cooling apparatus has at least one refrigerant tube disposed in the electric machine. The refrigerant tube is in thermal communication with the electric machine. An internal liquid is disposed inside the frame of the electric machine. The internal liquid is in thermal communication with the electric machine and at least one refrigerant tube. The refrigerant is at least partially a hot liquid refrigerant supplied from a floating refrigerant loop.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application60/565,461 filed Apr. 26, 2004, and is herein incorporated by reference.This application is related to U.S. patent application Ser. No.10/926,205 filed Aug. 25, 2004, and is herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with United States Government support underContract No. DE-AC05-00OR22725 between the United States Department ofEnergy and U.T. Battelle, LLC. The United States Government has certainrights in this invention.

BACKGROUND OF THE INVENTION

For vehicles using electric motors and power electronic inverters,two-phase cooling with the coolant changed from the liquid phase to thevapor phase is far more effective than using single-phase such as liquidto liquid heat transfer. The significant latent heat associated with thetwo phase heat transfer is the reason for making two-phase coolingattractive. This type of cooling addresses the need for increased powerdensity and associated higher heat fluxes in inverters and tractiondrive motors.

There are various water cooled stator frames available. The pressurethat the water jacket can take is not as high as what a certainrefrigerant such as R134a takes, as well as potential porosity problemsin aluminum castings causing leaks under high pressure. A totally newconcept of the electric machine frame design is presented in thisinvention.

The single phase cooling cannot be totally removed even in a two-phasecooling system. For example, in a motor the heat loss produced in thestator winding still needs to go through a single-phase heat transfer(i.e. thermal conduction) before reaching to the two-phase cooling zone.This invention presents a method that can enhance both the two-phase andthe single-phase heat transfer arrangements.

U.S. Pat. No. 5,271,248, issued to Crowe on Dec. 21, 1993, teaches adual cooling system for motors that removes heat using a standardrefrigerant cycle and heat exchangers.

BRIEF DESCRIPTION OF THE INVENTION

This invention presents the device and method for cooling electricmachines with hot liquid refrigerant in a floating refrigerant loop andusing an internal liquid such as oil for enhancing the cooling effects.The electric machine cooling apparatus has at least one refrigerant tubedisposed in the electric machine. The refrigerant tube is in thermalcommunication with the electric machine. An internal liquid is disposedinside the frame of the electric machine. The internal liquid is inthermal communication with the electric machine and at least onerefrigerant tube. The refrigerant is at least partially a hot liquidrefrigerant supplied from a floating refrigerant loop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment showing tubes cast in a frame and internalliquid level inside an electric machine.

FIG. 2 has tubes cast in the frame with certain tube portions exposedinside the frame.

FIG. 3 is a perspective view of a refrigerant tubing layout.

FIG. 4 is a sample frame for a HSUB motor with the wound stator corehaving right and left bearing brackets, additional axial excitationcoils with cooling holes, and internal liquid.

FIG. 5 is a sample rotor.

FIG. 6 shows minimal internal liquid level changes for a horizontalmachine mounted perpendicular to the vehicle's travel direction.

FIG. 7 shows internal liquid level changes for a horizontal machine asvehicle tilts to the left or right.

FIG. 8 shows the internal liquid scooper with or without grooves.

FIG. 9 shows a wavy surface, with or without grooves, formed into theend piece for internal liquid pick-up.

FIG. 10 is an example using a ball valve for controlling crossover flow.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of the invention using tubes 11 cast in aframe 12 and internal liquid level 14 inside electric machine 10 forcombined two-phase and single-phase cooling. Metal tubes withstand thehigh pressures required by the hot liquid refrigerant flowing in theframe 12. An internal liquid 16 such as a transmission or lubricationoil is filled at the bottom of the frame 12. Hot liquid refrigerant 17enters the electric machine 10 from a floating refrigerant loop (notshown) as described in co-pending U.S. patent application No. 60/565,461filed Apr. 26, 2004, herein incorporated by reference, and hot vaporrefrigerant 18 exits the electric machine 10 returning to the floatingrefrigerant loop. The hot vapor refrigerant 18 that exits the electricmachine 10 can be a mixture of refrigerant vapor and liquid depending onthe heat load imposed by the electric machine. The floating refrigerantloop can be a stand-alone loop having a dedicated pump and condenser.Or, the floating refrigerant loop can be integral with the vehiclerefrigeration system.

The frame 12 can be tied to the floating refrigerant loop for the totalthermal management system as taught in U.S. patent application Ser. No.10/926,205 filed Aug. 25, 2004, entitled “Floating Loop System forCooling Integrated Motors and Inverters Using Hot Liquid Refrigerant”,and U.S. Pat. No. 6,772,603 issued to Hsu et al. Aug. 10, 2004, bothherein incorporated by reference. The pump (not shown) in the floatingrefrigerant loop pumps hot liquid refrigerant 17 into the electricmachine 10 and heat is transferred from the internal liquid and theframe 12 into the refrigerant to evaporate the refrigerant beforeleaving the electric machine as hot vapor refrigerant 18. The hot vaporrefrigerant 18 is cooled and condensed in a condenser (not shown).

FIG. 2 shows more details about the frame 12. The metal tubes 22 arepartially exposed inside the electric machine frame 12. The arrangementallows the frame 12 to be sand cast or die cast. Various metal tubessuch as copper and aluminum tubes can be used as long as the castingdoes not damage the mechanical strength of the tube. The hot liquidrefrigerant 17 inlet side of the individual tubes can be welded orbrazed together to form a single fitting. The same manner can be usedfor the hot vapor refrigerant 18 outlet side of the tubes. Ribs 24 arecast in the frame 12 to allow certain portions of the tubes 22 to beexposed inside of the frame. Very small gaps may exist between the tubes22 and the frame 12. Certain portions of the tubes may make directcontact with the frame. Heat transfer of the inner surface and the outersurface of the tubes can be enhanced by adding commonly known surfacetreatments such as fins, pins, and reentrant cavities. Theseenhancements can be applied to the entire tubes or to portions of thetubes for obtaining the most heat transfer improvements.

As an example the layout of the refrigerant tubes 22 is conceptuallyshown in FIG. 3. In practice, all the sharp bends of the tubes 22 shouldbe in reasonably large radii for reducing the flow resistance.

FIG. 4 shows a sample frame with wound stator core 41, right 42 and left44 bearing brackets, additional axial excitation coils 46 with coolingholes 47, and cooling internal liquid level 48. For conventionalmachines no additional axial excitation coils exist. The inductionmotors may have rotor windings in a squirrel cage form. The figureserves as an example to show that possible heat sources can come fromboth radial and axial directions. The cooling of other components insidethe frame such as the excitation coils of a HSUB machine can be achievedthrough the liquid droplets. As shown in FIG. 4 the excitation coil 46is situated inside the bearing brackets 42, 44. The internal liquid 48can cool the bearing bracket. The cooling holes 47 around the bearingbrackets allow the liquid to sip into the excitation coil 46 for abetter thermal dissipation.

Because very small gaps may exist between the tubes and the frame, aninternal liquid such as a transmission or lubrication oil is filled atthe bottom of the frame. The rotor 52 having a shaft 54 shown in FIG. 5,as an example, picks up a small portion of the internal liquid (oil) atthe internal liquid level 58 and slings internal liquid droplets to thestator coils, parts inside the frame, and to the exposed tubes. Theinternal liquid will fill up the gap between the tube and the framethrough capillary effect. This helps the two-phase heat transfer in thetubes as well as the cooling of the windings and coils inside theelectric machine. The motor frame can dissipate the heat coming out fromthe stator core and the liquid droplets can carry the heat from thewinding end turns and the other components inside the frame back to thesump for cooling. The liquid droplets are cooled down in inside of frameand in the frame sump for recirculation.

Because when the electric machine is mounted in a vehicle, the coolingliquid level inside the frame changes according to the angle of thevehicle. FIG. 6 shows that if the machine is horizontally mounted but isperpendicular to the vehicle's traveling direction, the internal liquidlevel 68 changes very little when the vehicle goes uphill or downhill.

FIG. 7 shows that the internal liquid level 78 changes more for ahorizontal machine mounted along the vehicle's traveling direction. Thesurface of the end pieces of the rotor must be smooth except the regionsclose to the outer diameter of the end pieces with various pick uparrangement. This lowers the drag produced between the rotor end piecesand the liquid, while allowing distribution of fluid to upper portion ofthe windings, motor frame, and cooling tubes.

The machine frame can be used as a heat sink for cooling components thatare not suitable to be cooled directly by the refrigerant liquid andvapor.

In order for the rotor to pick up the liquid without a strong drag,various slingers for producing liquid droplets inside the frame aredisclosed. For a very high speed motor, a smooth rotor surface might dothe job sufficiently. For a relatively lower speed motor FIGS. 8 and 9provide certain options.

FIG. 8 shows that the outer periphery of the rotor 82 end pieces 84contains certain scoopers 85 with or without grooves 86 for picking upthe liquid 88 and slinging it. The depth of the scooper and the size andnumber of the grooves 86 depends on the speed of the rotor 82. The depthand the number of the grooves 86 reduce if the speed is high for thedrag reduction.

FIG. 9 shows the outer periphery of the rotor 92 end pieces 94 having awavy surface 96 with or without grooves 98. The depth and size of thewavy surface 96 and the size and number of the grooves 98 depends on thespeed of the rotor. The depth, size, and number of the grooves reduce ifthe speed is high for the drag reduction.

There are two options for supplying internal liquid to the electricmachine: one is a dedicated internal liquid supply for the electricalmachine, the other ties the internal liquid sump 104 with thetransmission oil sump 106 for fluid communication. The liquid level forthe tied-together option is only balanced slowly between the internalliquid sump 104 and the transmission sump 106 when the vehicle is in alevel position. This discourages the temperature exchange between thetwo sumps. With the internal liquid shared with the transmission liquidsystem, a free liquid circulation between the machine and thetransmission system is discouraged because the transmission liquid (oil)temperature is normally at a higher temperature (around 85° C.) than theinternal liquid temperature (can be below 55° C.) inside the electricalmachine. FIG. 10 shows an example for controlling crossflow between theinternal liquid sump 104 and the transmission sump 106 by using a ballvalve 102. When the motor is tilted the ball valve 102 stops thecrossover flow. When the motor is level a slow flow is allowed.

The invention has been described in terms of specific embodiments whichare indicative of a broad utility but are not limitations to the scopeof the invention. Additions and modifications apparent to those withskill in the art are included within the scope and spirit of theinvention.

1. An electric machine cooling apparatus comprising; an electric machinehaving a frame, stator, and rotor, at least one refrigerant tubedisposed in said electric machine, said refrigerant tube in thermalcommunication with said electric machine, an internal liquid disposedinside the frame of said electric machine, said internal liquid inthermal communication with said electric machine and said at least onerefrigerant tube, wherein the refrigerant in,said at least onerefrigerant tube is at least partially a hot liquid refrigerant suppliedfrom a floating refrigerant loop.
 2. An electric machine coolingapparatus according to claim 1 wherein said internal liquid is selectedfrom the group consisting of transmission oil and lubrication oil.
 3. Anelectric machine cooling apparatus according to claim 1 wherein saidrefrigerant tube material is at least one material selected from thegroup consisting of copper and aluminum.
 4. An electric machine coolingapparatus according to claim 1 wherein said at least one refrigeranttube further comprises at least one surface enhancement selected fromthe group consisting of fins, pins, and re-entrant cavities.
 5. Anelectric machine cooling apparatus according to claim 1 wherein saidframe further comprises ribs.
 6. An electric machine cooling apparatusaccording to claim 1 wherein said tubes are disposed having a gapbetween said tubes and said frame.
 7. An electric machine coolingapparatus according to claim 1 wherein said rotor further comprises atleast one end piece to sling internal liquid droplets into contact withinternal surfaces of said electric machine.
 8. An electric machinecooling apparatus according to claim 7 wherein said at least one endpiece further comprises at least one scooper.
 9. An electric machinecooling apparatus according to claim 7 wherein said at least one endpiece further comprises at least one scooper with grooves.
 10. Anelectric machine cooling apparatus according to claim 7 wherein said atleast one end piece further comprises a wavy surface.
 11. An electricmachine cooling apparatus according to claim 7 wherein said at least oneend piece further comprises a wavy surface with grooves.
 12. An electricmachine cooling apparatus according to claim 1 wherein said internalliquid is in communication with a transmission sump.
 13. An electricmachine cooling apparatus according to claim 12 wherein communicationbetween said internal liquid and said transmission sump is controlledusing a ball valve.
 14. A method for cooling an electric machinecomprising; flowing refrigerant through at least one refrigerant tubedisposed in an electric machine having a frame, stator, and rotor; saidrefrigerant tube in thermal communication with said electric machine,slinging an internal liquid disposed inside the frame of said electricmachine, said internal liquid in thermal communication with saidelectric machine and said at least one refrigerant tube, wherein therefrigerant in said at least one refrigerant tube is at least partiallya hot liquid refrigerant supplied from a floating refrigerant loop. 15.A method according to claim 14 wherein said internal liquid is selectedfrom the group consisting of transmission oil and lubrication oil.
 16. Amethod according to claim 14 wherein said refrigerant tube material isat least one material selected from the group consisting of copper andaluminum.
 17. A method according to claim 14 wherein said at least onerefrigerant tube further comprises at least one surface enhancementselected from the group consisting of fins, pins, and re-entrantcavities.
 18. A method according to claim 14 wherein said frame furthercomprises ribs.
 19. A method according to claim 14 wherein said tubesare disposed having a gap between said tubes and said frame.
 20. Amethod according to claim 14 wherein said rotor further comprises atleast one end piece disposed to sling internal liquid droplets intocontact with internal surfaces of said electric machine.
 21. A methodaccording to claim 20 wherein said at least one end piece furthercomprises at least one scooper.
 22. A method according to claim 20wherein said at least one end piece further comprises at least onescooper with grooves.
 23. A method according to claim 20 wherein said atleast one end piece further comprises a wavy surface.
 24. A methodaccording to claim 20 wherein said at least one end piece furthercomprises a wavy surface with grooves.
 25. A method according to claim14 wherein said internal liquid is in fluid communication with atransmission sump.
 26. A method according to claim 25 wherein fluidcommunication between said internal liquid and said transmission sump iscontrolled using a ball valve.